LTE (Long Term Evolution)-Advanced will be mainly described below, but the present invention is not particularly limited to this.
In the LTE-Advanced, carrier aggregation (CA) in which a plurality of frequency bands are combined, a plurality of cells in different sizes, CoMP (Coordinated Multipoint) that allows a plurality of base stations to coordinate with each other, and a combination of a plurality of different communication techniques are taken into consideration. An LTE-Advanced network has a heterogeneous network (HetNet) configuration.
In the LTE-Advanced, in order to optimize an operating cost and a maintenance cost of a network, so-called MDT (Minimization of Drive Tests) in which drive tests are automatically conducted, instead of conducting drive tests manually, is taken into consideration. The MDT described herein refers to operation in which a mobile communication device performs measurement on network performance in response to a request from a network-side apparatus, collects and records measurement data and reports the data to the network-side apparatus. Accordingly, the measurement data of the mobile communication device include position information about the mobile communication device and a network operator is able to optimize coverage of the network by referring to the position information.
Further, the MDT is classified into an immediate MDT and a logged MDT. The immediate MDT is executed by a mobile communication device that is in a connected state, and the logged MDT is executed mainly by a mobile communication device that is in a standby (idle) state. There is also a logged MDT to be executed by a mobile communication device in a connected state. Data collected in the MDT measurement are stored in a measurement log (MDT log) and are thereafter reported to the network-side apparatus. Collection of measurement information by the MDT enables a network operator to find a problem with coverage of a measurement area and to minimize artificial drive tests.
The network-side apparatus described herein may include various network-side apparatuses, such as an eNB (evolved Base Station), an HeNB (Home evolved Base Station), an RNC (Radio Network Controller), a GW (Gate Way), and an MME (Mobile Management Entity). These network-side apparatuses described herein are collectively referred to as a base station. The mobile communication device may include a cellular phone, a smartphone, a PC, a tablet terminal, and the like.
PTL 1 discloses a method for reporting an MDT log in an LTE system. Specifically, PTL 1 discloses an exchange procedure of a signal message for MDT between a base station and a mobile communication device. In PTL 1, among signaling radio bearers (SRBs) including SRB0, SRB1, and SRB2, SRB1 and SRB2 are used. Specifically, PTL 1 proposes a method in which the base station transmits a request message by SRB1 and the mobile communication device transmits a response message including an MDT log on SRB2.
PTL 2 discloses a method and a system in which not only a drive test result in a mobile communication device connected to a serving cell is reported to a base station but also information about a cell neighboring the serving cell is reported to the base station.
PTL 3 discloses a radio communication system in which a mobile terminal apparatus measures reception quality respectively from reference signals respectively multiplexed on a protect subframe whose transmission is suppressed by a macrocell and on a non-protect subframe whose transmission is not suppressed by the macrocell, and notifies a base station apparatus of the measured reception quality.